1. Field of the Invention
The present invention relates to an electrodeless discharge lamp unit that lights an electrodeless discharge lamp with an excitation coil wound round it by supplying high frequency electric power to the excitation coil and a lighting system and, more particularly, to an electrodeless discharge lamp unit that lights an electrodeless discharge lamp that is provided with an auxiliary tube.
2. Description of the Related Art
As related art of electrodeless discharge lamp units, those units disclosed in the following Japanese Patents are known:
(1) Japanese Patent Disclosure No. 8-329904 PA1 (2) Japanese Patent Disclosure No. 9-92013 PA1 (3) Japanese Patent No. 2548867 and PA1 (4) Japanese Patent Disclosure No. 7-22184
In Related Art (1), a technology to form a ring-shaped discharge in a luminescent tube was disclosed; that is, a heat resisting metallic fine conductor is kept in contact with the outer wall of a luminescent tube. After dielectric breaking a luminescent tube by applying high-tension to this metallic fine conductor, high-frequency current is applied to an excitation coil wound round the luminance tube so that a ring-shaped discharge is formed in the luminescent tube.
In Related Art (2), the bulb is in the double structure and a fine tube is formed in the outer bulb and the bottom of this fine tube is kept in contact with the outer wall surface of the inner bulb. Also, an electric starting conductor is arranged in the fine tube. This Related Art (2) can be said the technology developed from Related Art (1).
In Related Art (3), auxiliary current is injected into the luminescent tube through the partition wall between the auxiliary tube and the luminescent tube. In this Related Art (3), the technology to improve the starting ability by injecting auxiliary current was disclosed. Further, a ring-shaped discharge is formed in the luminescent tube by applying current to the excitation coil when forming auxiliary discharge.
Related Art (4) disclosed a method to surely obtain required auxiliary tube apply voltage and excitation coil current in the construction wherein the auxiliary tube is kept airtight separately from the luminescent tube airtight likewise Related Art (3).
However, in Related Art (1) and (2), the electrodeless discharge lamp unit is in a structure that a metallic conductor is kept in contact with the luminescent tube and so, the coldest portion is formed at its contact point. Therefore, it is difficult to obtain luminescent metallic steam pressure required for high efficient discharge. In addition, as the frequency heat cycle of lighting ON/OFF is applied to the metallic conductor and the tube wall of the luminescent tube, the tube wall of the luminescent tube can be cracked.
In Related Art (3) and (4), as the discharge lamp unit is in such a structure that the metallic conductor was not kept in contact with the luminescent tube, the above-mentioned problems are not generated or even when generated, its extent is less. However, the ring-shaped discharge is formed in the luminescent tube by forming auxiliary discharge in the auxiliary tube, only a luminescent tube of lower gas pressure than those disclosed in Related Art (1) and (2) can be started. In particular, even when the high-tension generating means disclosed in Related Art (1) and (2) was connected directly to the end of the auxiliary tube as disclosed in Related Art (4), starting ability of the lamp was not promoted at all.